Magnetron



4 Sheets-Sheet l ,l I I I\ INVENTOR. JOSEPH F. HULL AHO/flej TO WATER SUPPLY FIG. 1

March 24, 1953 J. F; HULL MAGNETRON Original Filed April 3, 1950 WAVE GUIDE OUTPUT J. F. HULL MAGNETRON March 24, 1953 4 Sheets-Sheet 2 Original Filed April 5, 1950 INVENTOR JOSEPH E HULL A/fwa In? March 24, 1953 J. F. HULL 2,632,863

MAGNETRON Original Filed April 5, 1950 4 Sheets-Sheet 5 INVENTOR.

JOSEPH F. HULL FIG.8

March 24, 1953 Original Filed\April 5, 1950 Fla? J. F. HULL MAGNETRON 4 Sheets-Sheet 4 FIG.6

INVENTOR.

JOSEPH F. HULL Patented Mar. 24, 1953 MAGNETRON Joseph F; Hu1l,=-Neptune, N. J.

-' Original" application April 3, "1950, *S erial" No.

153582. "L-Divided and this application January 31; -1952',-Serial=No. $569,572

.1 ZTCIaims.

(Cle315-39) fGranted underl Title BSFUZ secede tal-952), 1 sec. '-266 *This application is a division-bf application Serial 'No. 153;682'fifi1dApri1- 3; 1950. v The inventioir described" herein "may be manufactured and -used by or "for the Government for governmenta1 purposes; without'the payment of r-any royalty thereon.

This invention'relates' to electronic devices and vm'ore particularly "tmmagnetrons. glIn the' Patent 2;454;s37;-wh1ch was issued" to magnetron -*'structure -"empioying an inverted 1e'-and s1ot"type'-anode structure "giidled'loy a cathode. -ilnthis type of structure-" a number of electrical "modes eXist-which are close'together.

divergentthat the"high "current" portion' of the cavity". occupi'estoo small an area; 'thus' decreasring 'circuit'fficiencyf the number of-cavities his iarge';"thenumber of m'od'es is increased: and

tas a result there is-insufficient -mode "frequency Tseparation, Duetothe'fact"thattheinterdigital :magnetronds Y a "single? cavity resonator" and the ""wave'typemagnetron is a multi 'cavityresonator, i"it:is"ea'sy to show"wh "the'interdigitar magnetron *-"anodestructurecari beinverted "without" detriimentareffectsf on" mode separation and circuit "efficiency. Thisiis "not"true"for"the-wave type :"magnetron. Moreover, with the inverted interdi'gital magnetron; aiarge diameter "icavity can *i'l'vide agreater area for the'highcurrent flowyand fistili proVideshfiicient mode separation.

It is'ther'efore an oloject ofthist'inventiomto provide an improved ultraehigh frequency elec- "itricffdischargei.device-of thema'gnetrontype.

.jAnotherlobject"of'theinvention is to provide a magnetron structurewhereinf the: resonant" .sysitem permits" arjgre'atdegree *ofamodeseparation :ithus' increasing: the efitciency ofi'the magnetron structure;

'CTGkress on November "23,1948 thereis" showrr'- aviti es "are""used,"-the "cavity structure is "s;-

*Still another object of the'invention is td pro vi-de an inverted =magnetron structure employing "flan int'erdigital'typeanode.

*Further'objects of theinvention will appear to """those skilled in the'art to which it"perta-ins'; =both M by*'direct "recitation thereof as the description proceeds and -'by*-im'p1ication "from thecontext.

---R;eferring'r to the accompanying drawings in which like reference numerals indicate -sirnilar parts throughout the"-severa1--'views:

Fig; Iisv a cross-s'e'ction'a'l view of a magnetron embodying the present invention;

Fig. 2 isa perspective-"view showing 'the' detailed construction of the magnetron cathode and 1 *anode illustrated ifiFigl 1;

- FigBK-is a perspective vi'ew sho'wing the detailed construction-"of' -the magnetron anode shown-in Figs? 1" and 2 Fig: 4 is a *cross-secti'on'al vievw 'of ta tun'able Sic-magnetron embodying the present invention;

Fig; "51s a perspectivevi'ew' of another embodi- -ment--'of-the anode shown in Fig. 3;

Fig; 6 -isan*e1evationa1- view-"of a tunable mag- 'netron employing a preferred- 'embodiment' of .25- 'the magnetromaride;

Figi 7-" is a' ver'tical' cross-sectional view 'onan axial plane of theportion above line -A%A f0f the" magnetron 'shown ifi Fig; 6

Fig; 8 is a=- vertical" cross-*sectionai 'view onran axi'a1p1ane of the portion belovv line A-'-A of the magnetron shown irF-Fig! 7 -an'd Fig. 9 isa perspective view-showing the detailed construction or a preferred embodiment-of the anode employed *iri the magnetron shown in -Figs. 6;"7= and 8.

Referring now tc Fig. 1*-bfthe' accompanying drawing, there is shown-an inverted iiltraehigh frequency magnetron including a; r copper cylindrical casing ortubewwi th top and bottom end "plates I l and 12 which are weldedorptherwise hermetically sealed; to the inner 1 surface of said cylindrical-"casing.

--'-At. --approximate1y the central-'- portion'- '-ofsaid *wt'uloe there is; "provided an" anode structure 3 zzis which isshown in *perspective -detail"in'FigsL 2 and 3. "Anode structure I 3;'which=may-preferab1y consist of copper,--may be 'considered' -as'compris- 'f-ing' a pair of-spaced annulartopandfloottom' discs ""14 and I 5 which are axia11yaligned;=-and a'pIur'aI- to ity ofoppositelyyplacedsetsof uniformly spaced bars [6 extending-towardeachotherdrom the outer periphery or saiddiscs. *Uniformly spaced "bars "16*are circumferentially arranged around the outer "periphery -of '-said=1sdiscs in a---p1ane tFfpBrpendicuIar to= "the"- surfaces-thereof swas to interleave with each other. Each of these bars are of uniform length and width, the length of the bars being approximately equal to the spacing between said discs. Alternate bars such as H and I9 are joined to bottom disc I while the remaining alternate bars such as l8 and 2c are joined to top disc |4, so that if one goes around the anode structure in any one direction, alternate bars are joined to the same disc. These bars may be of uniform thickness but in order to achieve greater heat dissipation and higher frequency operation, these bars are tapered linearly in such a manner so that each bar is thicker at the joined end than at the opposite end thereof.

In order to support the anode structure centrally with respect to the tube, the inner periphery of annular anode discs Id and I5 are brazed to the outside surface of tubular member 2|, made of copper or other non-magnetic metal, which extends longitudinally from topend plate H to bottom end plate l2 through the center of the tube and is coaxial therewith. The region boundedby top and bottom discs |4 and IS, the portion of the outside surface of tubular member 2i therebetween and the interleaved bars is termed the magnetron resonant chamber.

Girdling and radially spaced from said bars is cathode 22 which is coated with an emissive material and which is held in position by channel housing 23. Said channel housing consists of lateral cylindrical wall 24 and top and bottom end discs 25 and 26. The inner periphery of top and bottom end discs 25 and 2B of said housing extend radially inward slightly beyond the circumferential emitting surface of cathode 22, as shown in Fig. 2, in order to provide cathode end shields, thus preventing electron leakage from the interaction space between bars 5 and cathode 22.

Within said channel housing and juxtaposed with said cathode there is provided a heater coil 21, one end of which is welded to channel housing 23. The other end of coil 2'! is insulated from channel housing 23 and is connected to end conductor 29 which extends through lateral wall structure of easing H], and is supported coaxially in glass seal 32. Cylindrical heat shields 32 are provided within channel housing 23 between cylindrical wall 24 and heater coil 21. End conductor 28 which is welded to channel housing 23 also extends through'lateral structure of easing ID and is supported coaxially in glass seal 3|. The direct-current high potential 35 is applied in the usual manner through end conductor 28 and alternating-current heater coil potential 36 is supplied between end conductors 2B and 29 to supply the heater current.

Within tubular member 2| and coaxially therewith is an inner conductor 31 which extends approximately half the length of the upper portion of said tubular member. A coupling loop 38 is located within the resonant chamber and has a stem extending radially inward through a hole 39 in tubular member 2|, and connects with the lower end of inner conductor 31. Thus, efiectively, tubular member 2| and inner conductor 31 comprise a coaxial output line for the magnetron. Door knob coupler 40 connects with the upper end of inner conductor 3! in order to couple radio frequency energy to output waveguide 4|.

Water or other liquid cooling of the anode structure may be effected by the provision of rigid inlet and drain pipes 5| and 42, respectively, which are arranged within the lower portion of tubular member 2| as shown. Water stopper 4 plug 43 is positioned within tubular member 2| between the lower end of inner conductor 31 and the upper end of inlet pipe 4| in order to prevent fluid from entering into the resonant cavity. Water flows continuously through inlet pipe 4| and the overflow is removed through drain pipe 42. Thus, at all times a jacket of water is provided in the lower portion of tubular member 2| between plug 43 and drain pipe 42 to dissipate the heat generated in anode structure l3.

In order to provide a uniform magnetic field. the magnetron of the present showing is provided with ring-like magnetic coils 44' which are conveniently situated exterior to casing l0. Girdling and radially spaced from the outer periphery of said coils is a cylindrical iron casing 45 which is joined to bottom end plate l2 of tube Ill! by means of studs 46 and 41. Holes are provided in said iron shell to provide convenient access to end conductors 2'8 and 29.

In order to provide radio frequency chokes to further decrease-the leakage of electromagnetic energy from the resonant chamber, there are provided a pair of cylindrical iron sleeves 48 and 49 which depend from the inner periphery of top and bottom end plates H and I2, respectively. Said sleeves respectively girdle the upper and lower portion of tubular member 2| and are coaxial therewith, and extend inwardly from both top and bottom members toward the anode for a distance approximately wave length of the operating frequency. The outer diameter of said sleeves are approximately equal to twice the diameter of the tubular member 2|.

That portion of the top and bottom end plates and i2 between the sleeves and tubular member 2| is composed of copper or any other suitable non-magnetic material, while the remainder of the top and bottom end plates is composed of iron. In this manner, the magnetomotive force is applied close to the region of the interaction space in order to minimize magnetic flux leakage. 'Ihus, a uniform magnetic field is efiectively applied to the interaction space in the proximity of anode l3.

The combined influence of the uniform magnetic field established by the coils 44 over the interaction space, the direct current electrical field due to the voltage applied between anode l3 and cathode 22 and the potential due to the space charge cloud of the electrons, cause the electrons emitted from cathode 22 to migrate between said cathode and anode in a circumferential path coaxial with the anode. Simultaneously, as the electrons are rotating, the anode segments are individually assuming a sinusoidal time varying potential such that each anode segment is 180 electrical degrees out of time phase with each adjacent segment. If the rotational velocities of the electrons are such that any one individual electron is always under a positive segment, synchronization is said to occur, that is, the electrons are keeping step with the electric field of the anode structure. It is well known that when said synchronization occurs, magnetron oscillations may be generated provided voltage and magnetic field are of proper value for the particular mode of operation which in the present instance is the one known in the art as the 1r mode.

In Fig. 4 there is shown a magnetron employing an anode l3 which differs from the anode shown in Fig. 3, only in that bottom anode dis-c I5 is axially movable for tuning the magnetron. The means for axially moving disc I5 consists of two rods 50 and 5| which extend through sleeve 49 attests and sealing bellows 52 to ball bearing knurled nut '53. Cylindricalchoke 54 is provided to prevent leakage of electromagnetic energy from the interaction space. As shown inFig. 5, the interleaved bars of anode E3, in addition to being tapered as shown in Fig. 3, may also be circumferentially tapered so that the teeth are wider at the joined ends than at the opposite ends thereof in order to achieve a. wider tuning range.

Figs. 6, 7 and 3 illustrate a tunable magnetron employing a preferred modification of the anode structure which is shown in detail in Fig. 9.

The tunable magnetron shown in Figs. 6, 7 and 8 includesan anode structure I I which is axially mounted within non-magnetic metallic shell I I I, this shell being welded to the upper pole piece I I2 as well as lower pole piece H3, as illustrated at H4, H5, H6 and I I1 respectively. As shown Fig. 9, anode structure H0 consists of a plurality of axially aligned annular discs having uniform outer diameters which are stacked one above the other and are equidistantly spaced from each other. With the exception of upper and lower anode end discs I 18 and H0, the inner diameter of the intermediate anode annular discs such as I20, i2 and I26 are also uniform. Circular shaped cut-outs I2iI are circumferentially and uniformly spaced around the outer periphery of each of said discs, thus providing uniformly spaced teeth I22. Said discs are positioned one above the other'so that the teeth of only alternate discs such as I23 and I25 and I24 and I26 are coplanar. As illustrated, bars I27 are in abutment with said coplanar teeth, one bar for each vertical row of coplanar teeth. Each of these bars are of uniform length, width and thickness, the length of the bars being substantially equal to the spacing between upper and lower anode end discs I I8 and H5.

Girdling and radially spaced from bars I2! is a cathode 22 which is coated with an emissive material on its inner surface and which is held in position by channel housing 26, said housing consisting of lateral outer cylindrical wall 24 and top and bottom end discs 25 and 26. The inner periphery of top and bottom end discs 25 and 26 of said housing extend slightly beyond the circumferential emitting surface of cathode 22 in order to provide cathode end shields, thus preventing electron leakage from the interaction or discharge space I23 of the magnetron between coplanar bars I21 and said cathode.

Channel housing 23 is rigidly held in place by three supporting rods, one of which is illustrated at I29, one end of each of said rods being welded to disc 25 and the other end being welded or brazed to inner metal casing I30 which is encompassed by outer ceramic shell I3I. Said shell is brazed to upper pole piece II2 as illustrated at I32 and I33. Both the inner casing I30 and the outer ceramic shell are hermetically sealed by annular cap I34.

Within said channel housing and juxtaposed with cathode 22 there is provided an insulated heater coil 21, one end of which is welded to channel housing 23. The other end of coil 21 is insulated from channel housing 23 and connected to end conductor I35 which extends through hole in cap I34 and is supported coaxially therein by glass seal I35. The directcurrent high potential I3! is applied in the usual manner through end cylindrical conductor I38 and alternating current heater coil potential I39 is supplied between end conductors I35 and I38 to supply heater current.

T26 In order to support anode structure H0 centrally with respect to cathode 22 and shell-III the inner diameters of all the stacked annular discs, with the exception of upper and lower anode end discs H8 and 9, are brazed to the outside surface of cylindrical casing I40 which is coaxial and concentric with shell III. The inner diameters of anode end discs H8 and *9 are slightly larger than the inner diameters of the intermediate annular discs. Tubular members MI and I42 are brazed to the inner diameters of end discs I I8 and 9, respectively, said tubular members being concentric and coaxial with cylindrical casing I40. Tubular members MI and I42 will hereinafter be referred to as the upper tubular member and as the lower tubular member, respectively. Thus, effectively, upper and lower tubular members MI and I42 are the outer conductors of a coaxial line, the inner conductor of which consists of the outer surface of cylindrical casing -I 40.

Positioned between the inner wall of upper tubular member I41 and the outer wall of cylindrical member I40 is a cylindrical sliding contact I43 which is adjustable for tuning the magnetron. Sliding contact I43 effectively is a short circuit for the coaxial line which includes upper tubular member MI. The tuning mechanism includes tuning knob I44, a non-magnetic driving screw I45, a shaft I46, the lower end of which terminates in the upper end of movable cylindrical flange I41 and is welded thereto, and metal bellows I48. Tuning shaft I46 is insulated from annular cap I34 and is centrally positioned by ceramic insulator I49 which is concentric and coaxial with inner casing I30 and outer shell I-3I.

The upper end of bellows I48 is brazed to the lower end of movable flange I4! while the lower end of the bellows is brazed to upper pole piece H2 at I50 and I15I, respectively. Sliding con tact I43 is supported in position by tubular member I52, the upper end of which is welded to movable flange I4'I. Well I53 is proportioned so as to allow the desired degree of vertical travel of sliding contact I 43.

The tuning mechanism is centrally positioned by ceramic mounting yoke I54 which is attached to outer ceramic shell I3I by studs I55 and I56 respectively. Since the non-magnetic screw I45 is fastened to the tuning knob, it either raises or lowers shaft I46 because of the threaded engagements I51 and I58, which are of opposite pitch. When tuning knob is rotated in one direction, it moves downward because of threads I51 and at the same time the tuning shaft moves downward with respect to the tuning knob because of thread I58. Thus, both movements combine to move shaft I46 downwards. Bellows I48, therefore, is lowered, which in turn causes the sliding contact I43 to move down, thus tuning the magnetron. The output of the magnetron is coupled to wave guide I59 from the coaxial line which includes lower tubular member I42.

In order to prevent leakage of electromagnetic energy from the interaction space between bars I21 and cathode 22, cylindrical chokes are provided in the usual manner as illustrated at I60.

I6I, I62 and IE3.

Water or other liquid cooling of the anode member I40 and is coaxial therewith. As here 7 shown, the cooling liquid spirally circulates within cylindrical casing I40 along spiral fluid .channel I66 and the overflow is removed through drain pipe I65. Thus, at all times a jacket of water is provided to dissipate the heat generated in the anode structure. Similarly, in order to .cool sliding contact I43 water or other cooling liquid is made to circulate within tuning shaft I46 by means of inlet pipe I61 and overflow pipe I58.

While the invention has been described with ,reference to several particular embodiments, it

comprising a cylindrical shell, an anode centrally positioned within said shell, said anode comprising a plurality of annular discs axially aligned one above the other, each of said discs having uniformly spaced teeth on the outer periphery thereof, the teeth of alternate discs being axially aligned and coplanar and having a bar in abutmen-t therewith, a cathode girdling said bars and radially spaced therefrom, said cathode and anode having a common longitudinal axis, a first coaxial line coupled to one end of said anode, a sliding contact between the inner and outer conductor of said first coaxial line, means connected to said contact for axially moving said sliding contact to vary the operating frequency of the magnetron, and a second coaxial line coupled to the other end of said anode for coupling the output from the magnetron.

2. An ultra-high frequency tunable magnetron comprising a cylindrical shell, an anode including a lurality of annular discs axially aligned one above the other, each of said discs having uniformly spaced teeth on the outer periphery thereof, the teeth of alternate discs being axially aligned and coplanar and having a bar in abut- ,ment therewith, a cathode gir-dling said bars and radially spaced therefrom, means supporting said anode centrally within said housing with respect to said cathode, an upper and lower pole piece mounted in spaced relation with respect to said anode and cathode, a first coaxial line coupled to the uppermost anode disc, a sliding contact between the inner and outer conductor of said first coaxial line, means connected to said contact for axially moving said sliding contact to vary the operating frequency of the magnetron, and a second coaxial line coupled to the lowest anode disc for coupling the output of the magnetron.

JOSEPH F. HULL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

